Name ___________________
PLATE TECTONICS EXERCISE
@2002 -- The information contained in this document is copyrighted.
This Lab has been modified from a lab created by Tom Brazianus – North Seattle Community College
Yellowstone National Park
I. Tracking Plate Movements using Hot Spots
The velocities of tectonic plate movements have been calculated in several
ways over the last 40 years. Recent satellite technology allows us to
determine precise distances and changes in distances on extremely fine
scales of time and space. We can determine current plate movements for
most areas of the globe.
In order to calculate AVERAGE plate movements over longer periods of
time, we must rely on other methods. The record of magnetic field
reversals in oceanic lava flows can be converted to a time clock by matching
the pattern of magnetic changes in these rocks with the same pattern
(radiometrically dated) in basalts erupted on land. By using magnetometers
on ships, scientists do not need to dive down and collect seafloor specimens
to test and to date; instead the magnetic record on the seafloor can be
determined from simple ship-board measurements. By knowing times and
distances, we can then calculate how fast the seafloor has spread away from
divergent plate boundaries.
Another major means of calculating plate velocities is tracking the volcanic
"footprints" of hot spots as tectonic plates move across them. We assume
that a "hot spot" originates from a relatively stationary source deep within
the Earth's mantle. As plates move, these deep-seated plumes "burn" new
spots on the plates. These spots might be volcanic islands in the ocean or
volcanic landforms on continents.
The hot mantle plume is like a lit match. Hold a piece of paper over it and it
will begin to burn a hole in that paper. Move the paper slowly and the match
will burn a series of holes in the paper, the oldest "burn" being the one
farthest away from the match. The "age" of the burns and their distance
from the match can tell us how fast the paper has moved over it. P.S.
DON'T TRY THIS AT HOME.
The Hawaiian Islands, and Yellowstone National Park are examples of "hot
spots." In this activity we will use readily available information for each of
these geologic paradises in order to estimate how fast three specific
tectonic plates have moved over the time of the last millions of years.
II. Hawaiian Islands Hot Spot:
The following geology lesson, images and activities are being used (with
permission) from "A Teacher's Guide to the Geology of Hawaii Volcanoes
National Park" (copyrighted by the Hawaii Natural History Association). It
has been modified extensively for use in this lab.
While visiting Hawaii in the 1960's, Tuzo Wilson, one of the
founders of the theory of plate tectonics, noticed some
interesting features about ocean islands. On a map of the Pacific
basin, he found three linear chains of volcanoes and submarine
volcanoes (seamounts). As shown below, these are the (1) Hawaii
Islands -Emperor Seamounts; (2) The Pitcairn Island - Tuamotu
Group; and (3) the Macdonald Seamount - Austral Group. Notice
that the eastern most island or seamount of each chain is
volcanically active.
As we can see, although separated by thousands of miles, the
three linear chains are parallel to each other. Of the three, the
Hawaii-Emperor seamount chain was the most well known. Wilson
reviewed the reports that had been published on these island
chains and recorded the age of each island in the Hawaiian chain.
An interesting pattern emerged. For each chain, the islands
become progressively younger to the southeast. The extreme
southeast end of each chain is marked by active volcanoes.
Wilson proposed that the Hawaiian islands formed successively
over a common source of magma called a hot spot. The Island of
Hawaii is currently located above the hot spot.
Hot, solid rock rises to the hot spot from greater depths (see the
sketch below). Due to the lower pressure at the shallower depth,
the rock begins to melt, forming magma. The magma rises through
the Pacific Plate to supply the active volcanoes. The older islands
were once located above the stationary hot spot but were carried
away as the Pacific Plate drifted to the northwest
Image Source:
Eruptions of Hawaiian Volcanoes: Past, Present, and Future: U.S.
Geological Survey General Interest Publication.
.
HOT SPOTS AND MANTLE PLUMES
An Activity by Steve Mattox
Directions: Use the map and the following information to determine
the rate of motion of the Pacific Plate over the Hawaiian hot spot.
The volcano that formed the Island of Niihau is 4.89 million years
old.
Rate is the distance traveled over a period of time. The distance
traveled is equal to the distance from the present location of the
hotspot (southeast Hawaii) to Niihau. Time is the age of the island.
Question #1
Start by measuring the distance from southeast Hawaii to Niihau.
Use the scale on the map. The distance is ________________ km.
Question #2
To determine the average rate of motion for the Pacific Plate, divide
the distance to Niihau by the age of the island. The rate of plate
movement is _____________________ km/Ma (kilometers per
millions of years).
Question #3
Convert your answer to cm/yr (move the decimal to the left 1
place). The rate of Pacific Plate movement is _____________
centimeters per year.
Question #4
Using this rate, how far will the Pacific Plate move in 50 years?
____________cm
Question #5
Repeat the exercise above using the island of Molokai instead. From
the distance and age of this island, the rate of Pacific Plate
movement is ___________ centimeters per year.
Question #6
Is this rate different than the rate calculated using Niihau? What
might be one good reason why the rate would be different?
__________________________________________________
Question #7
What direction is the Pacific Plate traveling?
_________________
This next activity determines the average rate that the Pacific Plate has
moved over the last 65 million years.
The ages of the islands and seamounts increase with distance away from the
Hawaiian hot spot. This table shows these ages and distances for islands
and seamounts in the Hawaiian - Emperor chain.
Seamount or
Island
-----Suiko
Koko
Midway
Necker
Kauai
Distance (km)
------------4,860
3,758
2,432
1,058
519
Age
(Million Yrs)
--65
48
28
10
5
Question #8
Plot this data on the graph below. Once the points are plotted on the graph,
use a ruler to draw a straight line that starts at the origin and most closely
goes near all the data points (this is called a "best-fit" line). Determine the
slope of the line (pick any point on the line and divide the distance value by
the time value). This slope is equal to the average rate of plate motion. As
determined from your work, this rate is __________________ kilometers
/ million years.
Question #9
Convert your answer to cm/yr (centimeters / year): __________________
Question #10
Has the Pacific Plate been moving slower or faster over the last 5 million
years than it has in the past? Explain. ____________________________
Question #11
The trajectory of plate motion points toward Hokkaido on the northern part
of the Japanese Island chain, 6,300 km (3,900 mi) away. A subduction zone
offshore of Japan consumes the Pacific plate, which is partly melted to
create the volcanoes of Japan. If the "Plate Tectonic Express" operates
without change, the Big Island of Hawaii will be headed down the Japanese
trench. How long will it take Hawaii to reach Japan? Show your work.
6300km ÷ (Answer to Question #9 km/yr) = ? yrs
_______________________________yrs
III. Yellowstone National Park:
Hot spots may occur on continental lithosphere as well as
oceanic lithosphere. For example, Yellowstone National
Park is a huge volcanic caldera (collapsed summit of a
volcanic cone) which we believe had a culminating eruption
some 600,000 years ago. This is only the latest in a
series of major caldera-forming eruptions that have
traveled across the pacific northwest during the last 16
million years. In fact, we can track the movement of this
still-active volcanic hot spot as it has shifted from
Oregon through Idaho (creating its Snake River Plain
Volcanic Province) into Wyoming.
In actuality, the hot spot is stationary. It is the North
American plate which is moving across it. How fast is the
plate moving? We can apply the same method as before
in order to calculate this rate. Study the map below to
determine the distance from the current hot spot to the
12.5 million year old Bruneau-Jarbridge Caldera in
southern Idaho.
Old Faithful
Yellowstone National Park
Snake River Plain - Yellowstone Eruptive Centers
LC = 0.60 Ma Lava Creek Tuff
AF = 7.48 Ma tuff of America Falls
MF = 1.29 Ma Mesa Falls Tuff
KC = 9.17 Ma tuff of Kyle Canyon
HR = 2.00 Ma Huckleberry Ridge Tuff LR = 8.75 Ma tuff of Lost River Sinks
H = 4.49 Ma tuff of Heise
Ch = 9.34 Ma tuff of Little Chokecherry Canyon
Ek = 5.37 Ma tuff of Elkhorn Springs
AV = 10.09 Ma and 10.27 Ma tuff of Arbon Valley A & B
WC = 5.81 Ma tuff of Wolverine Creek Tw = 8.6 to10 Ma Twin Fall Caldera
CC = 5.94 Conant Creek Tuff
Br-Ja = 10.0 to 12.5 Ma Bruneau-Jarbridge Caldera
BC = 6.19 Ma tuff of Blue Creek
Ow-Hu = ~13.9 to 12.8 Ma Owyhee-Humbolt Caldera
W = 6.19 Ma Walcott Tuff
M = 16.1 Ma McDermitt Caldera
ES = 6.57 Ma tuff of Edie School
Question #12
Using the Yellowstone Hot Spot calculate how fast is the North American
plate moving? Show your work. Give your answer in centimeters per year.
Rate = (distance mi) x (1.61 km/mi) x (100,000 cm/km) ÷ (time my) ÷
(1,000,000 yr/my) = ______ cm/yr
_____________cm/yr
Question #13
In what direction is the North American plate moving?
____________________
Question #14
Where do we expect the hot spot to be in another 12.5 million years?
___________________________________________________
Conclusion
What are two things that you can figure out about tectonic plates from the
observations of HotSpots? ___________________________________
_________________________________________________________________________________________________________________
The End